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(1) Field of the invention
The present invention relates generally to a rubber crawler.
(2) Description of related art
From EP-A-0.118.912 a rubber crawler is known comprising an endless rubber belt driven around a toothed sprocket wheel and intermediate wheel. In the interior of the rubber crawler, distributed over the internal circumference of the belt, between the sprocket wheel and intermediate wheel, supporting rolls are provided for supporting the rubber belt. In longitudinal direction of the belt, at a regular distance from each other and parallel to each other, a plurality of metal core elements are embedded to drive the rubber crawler around the sprocket wheel and the intermediate wheel. Each metal link contains a basis with a center, the basis extending in transverse direction of the rubber belt, the center of the basis comprising a guiding. On both sides of the guiding a protrusion which protrudes towards the inner surface of the rubber belt, is provided in such a way that protrusions of successive metal links form the running surface for the supporting rolls. In order to render the running surface as continuous as possible, the protrusions are elongated in longitudinal direction of the crawler and extend in longitudinal direction of the rubber belt with respect to the metal link. The space between the basis of the metal link and the bottom side of the protrusion is at least partly filled with rubber.
The rubber crawler disclosed in EP-A-118.912 however presents the disadvantage that its stiffness in the bending direction of the crawler is too large, which leads to the formation of cracks and causes fatigue fractures in the rubber belt especially in the rubber phase located between the metal links, during use of the rubber crawler.
The inventions, according to one aspect, provide a rubber crawler with which the formation of the above described cracks and fatigue fractures can be decreased.
This is achieved according to the claimed inventions which provide, in accordance with one aspect thereof, a rubber crawler arrangement in which first and second protrusions respectively show, on opposite sides of the metal link and in transverse direction of the rubber crawler, a first and second front surface which extend from the basis of the metal link in upward direction thereof. Both the first and second front surface slantxe2x80x94taken in longitudinal direction of the crawlerxe2x80x94in opposite directions with respect to the basis. The slope of the first and second front surface with respect to the basis is smaller than 90xc2x0, so that the metal links can be embedded in the rubber crawler in such a way that the space between the front surface of the protrusions and the inner surface of the rubber belt remains almost free of rubber.
The top surfaces of the first and second protrusions have, taken in longitudinal direction of the crawler, a length Wt which is smaller than the width of the basis Wb, taken in longitudinal direction of the crawler, so that the protrusions do not extend with respect to the metal link. Because of the limited length of the protrusions and the absence of a bond between the protrusion, in particular the front surface thereof and the rubber belt, a larger free space remains between the protrusions of successive metal links. In that way on the one hand a reduction of the minimum possible bending radius of the rubber crawler can be obtained, while simultaneously the bendability and flexibility of the rubber belt in the moving direction of the crawler can be improved. Simultaneously, evacuation of stones and sand which may end up between the successive links during use of the rubber crawler can be improved. Also, because of the absence of a bond between the front surface of the protrusion and the rubber belt, stresses on the rubber of the belt caused by the tilting of the links within the belt, which lead to the formation of cracks and fatigue fractures, can be reduced.
The slopes xcex1 and xcex2 of the front surfaces of the first and second protrusions with respect to the basis are geared to the length of the running surface of the first and second protrusions Wt in such a way that the top surfaces of the first and second protrusions within one and the same metal link show an overlap O1 in transverse direction of the crawler which is  greater than 0, and the top surfaces of the first and second protrusions of successive metal links show an overlap O2 in transverse direction of the rubber crawler which is also  greater than 0. Herewith O1 and O2 and the length Wt of the top surfaces of the first and second protrusions, taken in longitudinal direction of the crawler, are chosen such that
O1+O2=2Wtxe2x88x92P
in which P is the distance between the centers of two successive metal links.
By gearing the angles xcex1 and xcex2 to the length Wt of the top surfaces of the first and second protrusions, it is possible to limit Wt in such a way that the protrusions taken in longitudinal direction of the rubber crawler do not extend with respect to the metal link, while maintaining an overlap between the protrusions within one link and between successive links and thus maintaining continuity of the running surface of the supporting rolls. Consequently, Wt is smaller than the width of the basis Wb, taken in longitudinal direction of the crawler. Because the length of the top surfaces of the protrusions is limited, it is possible to positively influence the bendability and the life time of the rubber crawler. By the particular mounting of the protrusions and improved continuity, the running surface of the supporting rolls can be optimized and vibrations caused by the movement of the supporting rolls over the running surface of the metal links can be kept under control.
The inventions described and claimed herein provide a rubber crawler with an improved flexibility in the moving direction of the crawler, in which the risk to the occurrence of cracks or fatigue fractures in the rubber can be reduced. At the same time an improved evacuation of materials which may end up between the links during use of the rubber crawler is made possible. Due to the improved continuity of the running surface of the supporting rolls, vibrations caused by a discontinuous contact of the supporting rolls with the successive metal links can be diminished correspondingly. Thus, with this invention a simultaneous improvement of the flexibility of the crawler and the evacuation of outside materials from the crawler can be obtained, as well as an optimization of the continuity of the running surface of the supporting rolls.
O1 is preferably substantially equal to O2 to obtain a running surface for the supporting rolls with an optimal continuity.
Preferably also the length of the running surfaces of the first and second protrusions Wt is larger than or equal to Ws, Ws being the width of the sprocket of the metal part, in order to provide a sufficient overlap between protrusions of successive metal links even in the case of a rubber crawler with a narrow sprocket.
To allow the stabilization of the metal link in the rubber belt to be improved, without sacrificing the bendability and flexibility of the rubber crawler, the first and second wings preferably have a substantially constant width over their entire length (WW2 below and WW1 on top), measured in the longitudinal direction of the rubber crawler.
To simplify the production process of the metal links and the rubber crawler the angle a between the front surface of the first protrusion and the basis is preferably substantially equal to the angle xcex2 between the front surface of the second protrusion and the basis, and the length Wt of the first protrusion is equal to the length Wt of the second protrusion.
Preferably the first and second protrusions have, on a position where they pass into the basis, taken in longitudinal direction of the crawler, a width Wb, which is substantially equal to the width of the wing WW2. This feature allows an approximately seamless passing of the protrusion into the basis and a substantial, often a complete support of the basis of the protrusion by the basis of the metal link, thus leading to an improved transfer of forces exerted on the protrusion to the basis of the metal link and an improved durability of the protrusions.
In the rubber crawler of this invention the length Wt of the top surfaces of the first and second protrusions is preferably smaller than or equal to the width of the bottom sides of the first and second wings (WW2), measured in longitudinal direction of the rubber belt. Thus, an improved stabilization of the metal link in the rubber belt without endangering the flexibility of the belt in doing so can be achieved.
If so desired one or more holes can be provided in the first and second wings for purposes of further reducing the weight and the cost of the metal links and providing an improved anchoring of the links in the rubber of the belt.
From EP-A-490.829 a rubber crawler is known in which each metal link contains a central sprocket, and in which protrusions are provided on both sides of the sprocket. The protrusions comprise a first pair of flaps which are located on a short distance from each other and extend parallel to each other in longitudinal direction with respect to one side of the metal link, and a second pair of parallel flaps which are distant from each other and extend in opposite direction with respect to the metal link. To improve the continuity of the running surface of the supporting rolls, the first flaps of a first link are located between the second flaps of a subsequent link. However because of the presence of the flaps, the rubber crawler of EP-A-490.829 shows an even larger stiffness and an increased risk to the occurrence of cracks and fatigue fractures than the one disclosed in EP-A0.118.912.
The inventions also provide processes for the manufacturing of a rubber crawler.
In the mold a first and a second oblong holder are mounted parallel with each other in longitudinal direction of the rubber crawler. Each holder contains a plurality of parallel partitions, between which holes are provided for receiving the protrusions of the metal links, the protrusions resting with their top surfaces on the bottom of the holder. The partitions make sure that the metal links are held on a fixed distance from each other. The partitions of the first and second holders are, taken in transverse direction of the crawler, arranged in line, so that the metal links are received in transverse direction of the crawler. The length of a partition measured in longitudinal direction of the holder defines the distance between successive metal links. The length of the hole measured in longitudinal direction of the holder is chosen such that there is not too much play between the partitions and the protrusion, in order to prevent that the protrusions would be covered with rubber. After the metal links have been positioned in the holders, the mold is closed and filled with rubber.
After the rubber has been vulcanized, the crawler is removed from the mold and the holders are removed from the crawler.
The inventions are further elucidated in the appended figures and description of the figures.